The invention relates to a method and a device for joining two transfer or laminating film webs, which comprise a thermoplastic carrier film and a decorative layer.
In the processing and use of transfer films and laminating films, film portions must often be joined to each other in order to assemble correspondingly longer “run lengths” from shorter film webs or strips.
Particular run lengths result both from customer requirements, for example to increase productivity using very long cutting rolls, and from the demand to minimize waste, since setup times or downtime, in particular for changing the rolls, are reduced.
In the “in-house” production and processing of films, there is likewise the need to join film webs to each other to increase productivity, minimize waste and reduce setup times, downtime and start-up processes.
The most common method is joining, also called “splicing”, by means in particular of manually affixed adhesive tapes. Here the corresponding films are glued together using self-adhesive tapes customary in the trade. Laminating or transfer films (films coated on one side with a transfer layer) are typically glued on the uncoated side of the film. The width of the adhesive tape is typically in the range of from 2 to 5 cm. Typical thicknesses for adhesive tapes lie in the range of from approximately 30 to 130 μm.
Splicing with adhesive tape has proved its worth in recent years and offers a range of advantages. The method is cost-effective, can be carried out with a relatively high register accuracy of the films relative to each other and the splice, i.e. the joining point or joining seam, has high strengths, in particular tensile strength in the direction of travel of the films. In addition, colored adhesive tapes are often used to characterize particular types of splices and to make them visually distinguishable.
However, splicing by means of adhesive tapes has a range of disadvantages.
In the stamping of individual images, these individual images or motifs, i.e. the panels, are arranged in a particular layout on the film, in particular in regular lines and tracks. The panels to be stamped usually lie so close together that the adhesive tape lies in the area of the stamping zone and at the same time in the area of the panels to be stamped such that these overlapped panels cannot be stamped and are lost. In particular this can lead to stamping errors and/or to contamination of the stamping tool by the adhesive tape or by the adhesive of the adhesive tape emerging at the edge. The splice is therefore detected and the film is advanced, whereby there is a loss of material and productivity is reduced.
In the stamping of individual images on parallel tracks, it is also required that the splice points arrive at the stamping unit at the same time, as the stamping process must be interrupted on all tracks or all panels must be skipped at the same time and all these panels are lost. If the splices are at different points in the films, the stamping process is to be interrupted for longer times or must be repeated a number of times.
In the stamping of individual images by means of multiple applications, additional problems arise. Here the repeat of the individual images, i.e. the space between the individual images, must agree very exactly. For this reason, only film pieces with the same repeat can be spliced together.
Within spliced rolls it is possible that, at the splice point—caused by the higher pressure—cold adhesive emerges at the edge of the splice tape or the roll is “blocked”, i.e. adjacent windings on the roll stick together.
Using adhesive tape splicing requires a higher outlay on control engineering.
The use of narrower adhesive tapes with a width of less than 1 cm is generally not possible because the strengths required, in particular tensile strengths during processing, cannot be reliably achieved with narrow adhesive tapes and the splice point can also open due to the tensile forces during winding or inside the roll.